1) Field of the Invention
The present invention relates to a printing head for an ink-jet printer, and more particularly, to a drop-on-demand type ink-jet printing head.
2) Description of the Related Art
As is well known, an ink-jet printer is a typical non-impact printer having a simple construction and suitable for chromatic color printing. Generally, an ink-jet printing head for the ink-jet printer includes a head body having a plurality of pressure chambers formed therein, and a plurality of orifices communicating with the respective pressure chambers, a plurality of piezoelectric actuators arranged in the head body to thus partially define the pressure chambers. respectively, and an ink source for supplying an ink to the pressure chambers, which are filled with the ink. When each of the piezoelectric actuators is selectively energized on the basis of image data obtained from a word processor, a personal computer, or the like, a volume of the corresponding pressure chamber is instantly changed and thus an ink-jet drop is ejected from the orifice thereof, and accordingly, an image is recorded on a sheet of paper by the ejected ink-jet drops.
Two drive modes for the ink-jet printing head are known in this field; a Kaiser drive mode and a shearing drive mode.
In the Kaiser drive mode as disclosed in, for example, Examined Japanese Patent Publications No. 53(1978)-12138 and No. 57(1982)-20904, the piezoelectric actuator, which is constructed as a plate-like bimorph type actuator, is arranged such that it defines a top wall of the pressure chamber, and when this plate-like bimorph type piezoelectric actuator is electrically energized, it is instantly bent in such a manner that a volume of the pressure chamber is reduced, and accordingly, an ink-jet drop is ejected from the orifice. The plate-like bimorph type piezoelectric actuator must have a relative large wide area, to enable a pressure to be generated in the pressure chamber that will cause the ejection of the ink-jet drop from the orifice. Accordingly, the pressure chambers must be disposed at a considerably wider pitch than a fine pitch at which the orifices are located. For this reason, in the Kaiser drive mode ink-jet printing head, a plurality of relative long passages must be formed, to connect the pressure chambers to the respective orifices, and thus, the Kaiser drive mode ink-jet printing head has a relatively large size, and has a further disadvantage in that a pressure loss occurs due to the long passages formed between the pressure chambers and the orifices.
In the shearing drive mode as disclosed in, for example, Unexamined Japanese Patent Publications No. 63(1988)-252750, and No. 63(1988)-247051, the pressure chambers are disposed side by side, and the piezoelectric actuators are arranged such that they form side walls of the pressure chambers. To generate a pressure at one of the pressure chambers, and eject an ink-jet drop from the orifice thereof, the piezoelectric actuators or side walls of the pressure chamber concerned are electrically energized, and thus instantly deformed, to thereby reduce a volume of the pressure chamber. The deformation of the side walls is carried out in such a manner that these side walls are subjected to a shearing stress. Of course, in this arrangement, the energizing of the piezoelectric actuators or side walls of the pressure chamber concerned affects a pressure of the ink held in the side pressure chambers adjacent thereto. Namely, the ink cannot be statically held in each of the pressure chambers, and thus it is difficult to constantly carry out a stable printing operation. Also, the shearing drive mode ink-jet printing head is disadvantageous in that ink-jet drops cannot be simultaneously ejected from the two adjacent orifices, because the two adjacent pressure chambers are bounded by the common piezoelectric actuator or side wall therebetween. Further, production of the shearing drive mode ink-jet printing head is costly because fine and precise cutting work is required when forming pressure chambers having a width of several tens of microns.